The present invention relates generally to medical devices and, more particularly, to an acetabular bearing assembly of a total hip joint prosthesis for minimizing or eliminating the production of wear debris resulting from relative motion at the interface between the acetabular shell and polymer bearing insert portions of a modular acetabular bearing assembly.
Hip surgery for the replacement and repair of hip joints has become relatively commonplace in recent years. Prosthetic hip joint devices are available from a variety of manufacturers. Such hip prosthetic systems, when properly installed, approximate a patient""s natural hip movement.
Typical hip joint prostheses contain a femoral component and an acetabular component. The femoral component has an intramedullary portion which is fixed to the femur of a patient. The femoral component also has an attached ball portion which allows articulation, restricts dislocation or subluxation, and transfers loads to the acetabular component. The acetabular component may be unitary, including a concave bearing surface to articulate with the ball, and a fixation surface for attachment to the acetabulum. Acetabular components may be of modular construction, including a bearing insert portion and an acetabular shell portion which receives the bearing insert and is affixed to the acetabulum of a patient.
Currently available modular acetabular components use a polymeric material for the bearing insert. Such currently available modular acetabular components suffer from a tendency toward relative motion between the bearing insert and the acetabular shell portion. Such relative motion can cause wear and the generation of small particles from the polymeric bearing insert. Such wear can lead to failure of the hip joint prosthesis and lysis of the surrounding bone.
Various attempts to solve this problem include elaborate and often costly locking systems to minimize relative motion at the interface between the bearing insert and the metal acetabular shell portion. In addition, such attempts at solving this problem have often not been modular and therefore have lost the advantages of modularity, including the possibility of using screws to fix the metal acetabular shell portion to the acetabulum.
Accordingly, there is a need for a modular acetabular bearing assembly which either minimizes or eliminates the production of wear debris resulting from relative motion at the interface between the polymer bearing insert and metal acetabular shell portions of hip joint prostheses.
The present invention fulfills the aforementioned need by providing an acetabular bearing assembly for a total hip joint which either minimizes or eliminates the production of wear debris that results from relative motion at the interface between the polymer bearing insert portion and metal acetabular shell portions of a total hip joint prosthesis.
In one embodiment of the present invention, an acetabular bearing assembly is provided, which includes (1) an acetabular shell having an outer convex surface for fixation to a surgically prepared acetabulum and an inner concave surface, and (2) a composite bearing insert having a polymer layer and a metal layer, wherein the polymer layer forms a concave bearing surface shaped to receive a ball-end of a stem, and wherein the metal layer forms a convex surface to interlock with the concave surface of the acetabular shell. The composite bearing insert is constructed so that the metal layer and the polymer layer are interlocked to minimize relative movement therebetween. The acetabular bearing assembly may be configured such that the composite bearing insert contacts the acetabular shell only through metal-to-metal contact. In one embodiment of the invention, the composite bearing insert and metal acetabular shell are interlocked through a plurality of interlocking dovetails. In various other embodiments of the invention, the acetabular shell and composite bearing insert are interlocked through a locking arrangement selected from the group consisting of: a locking taper, a screw fastener, a pin fastener, a locking bayonet and a snap ring.
The present invention also includes a technique for constructing acetabular bearing assemblies. In one embodiment of the present invention, the method includes (1) constructing a metal layer in the form of a metal endoskeleton with a first locking mechanism and a second locking mechanism, wherein the first locking mechanism is disclosed on a concave portion of the metal endoskeleton and the second locking mechanism is supplied on a convex portion of the metal endoskeleton, (2) filling at least a portion of the metal endoskeleton with a polymeric powder, (3) molding the polymeric powder upon and within the metal endoskeleton to form and lock the polymeric bearing layer to the metal endoskeleton, and (4) locking the metal endoskeleton to an acetabular shell. In various embodiments of the invention, the locking mechanisms between the endoskeleton and the acetabular shell may include a locking taper or threaded surface.
The details of the various embodiments of the present invention are set forth in the accompanying drawings and description below. Numerous additional features and advantages will become apparent from a review of the following details of various embodiments of the present invention.